The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Today, many mobile devices (smartphones, tablet personal computers, etc.) are capable of determining their locations using one or more of various locating techniques. For example, some mobile devices are equipped with a Global Positioning System (GPS) chip to determine the latitude, longitude, and elevation of the mobile device based on signals received from several GPS satellites. Some mobile devices are instead (or additionally) capable of determining location using signals from fixed or semi-fixed terrestrial elements having known locations, such as cellular infrastructure elements (e.g., cell towers), WiFi access points (APs) or “hotspots,” etc. These locating techniques based on fixed or semi-fixed terrestrial elements may be especially useful if other techniques such as GPS are unavailable. For example, signals from WiFi APs and/or cell towers may be used to locate a mobile device when the mobile device is indoors and unable to receive a GPS signal, or does not include a GPS chip. Typically, the mobile device receives a signal from a WiFi AP or cell tower, and requests a location of the observed AP or cell tower from a location provider such as Google, Apple, or Skyhook. Requests are typically sent to the location provider because the set of locations of all possible transmitters would be too large for typical mobile devices, and due to constant change would be difficult to keep up-to-date.
Relying on fixed or semi-fixed terrestrial elements such as cell towers or WiFi APs to locate a mobile device suffers from various drawbacks. For example, cell towers may be sparsely located in certain areas, making accurate positioning difficult. Cell towers may also be relocated several or more times a year (e.g., identifiers of cell towers in a particular region may be remapped), which can cause a location provider to report incorrect locations until the cell tower locations in a database are updated. While WiFi APs may be more densely located than cell towers, APs may, in some instances, be relocated even more often than cell towers. For APs that move frequently (e.g., APs used during conferences or other temporary events), maintaining a fresh location database may be particularly difficult. Moreover, for privacy reasons, some AP owners prevent their APs from being used to locate mobile devices.